The present invention relates to a gaseous flow distribution means for use in or in connection to a sterilizer chamber of the type in which a gaseous medium, such as steam or air, is brought to circulate.
Sterilizers for heat treatment of various articles, which articles are placed in a chamber in a pressure vessel, are widely used for sterilising objects both in pharmaceutical industry and for hospital or other similar use. One such arrangement for sterilising is described in U.S. Pat. No. 4,576,792.
In a chamber in a pressure vessel, e g an autoclave, articles are heat treated by water, which is sprayed over the articles through nozzles and which supplies heat to or removes heat from the articles. Simultaneously, a gaseous medium, e g a mixture of steam and air, is forced by an impeller to flow through the articles in countercurrent to the water.
Since the temperature of the articles is critical to ensure a successful sterilisation, the need of even temperature distribution in the chamber is well known.
In an autoclave as the one set out in U.S. Pat. No. 4,576,792, there are at least two problems involved that makes the temperature throughout the chamber unevenly distributed.
Primary, the flow of gaseous medium that is forced to flow through the articles, does not have the same intensity throughout the chamber. This problem is of course also occurring in sterilizers of the kind using only a gaseous medium, and no liquid, for sterilising. The variations in the flow of the gaseous medium will cause an uneven temperature distribution both between different articles and within one article. This is a considerable problem, especially when dealing with articles that are sensitive to being heated during longer periods of time, such as certain biologically active materials. To ensure that all articles are sterilised, the procedure will have to continue for a certain period of time that is adapted to the articles being least exposed to heat, which will risk to cause damage to those articles that are mostly exposed to the heat.
Secondly, the liquid flow is not constant through the chamber, or even in one cross-sectional area of the chamber. This is due to the fact that the nozzles, which are normally provided in the top of the chamber, spread liquid in a cone-like shape from the outlet of the nozzles. The liquid is thus not homogeneously brought over the articles to be sterilised. Instead, certain zones of articles or parts of one article obtain different temperatures due to the uneven distribution of liquid. Much liquid is also spread to the walls of the chamber, where it does not contribute to the sterilisation procedure. Also, the nozzles are rather expensive.
The present invention solves the first problem as set out above by providing a gaseous flow distribution means according to the preamble, characterised in cover means covering essentially a section area of said chamber, said area being disposed in an angle to the flow of gaseous medium. Said cover means are further defining slits, through which gaseous medium is allowed to pass. Said slits are shaped and distributed over the area so as to control the gaseous flow inside said chamber in a predetermined manner.
In that the slits are distributed over the area of the chamber, the gaseous medium can pass through slits in certain chosen parts of the area, which provides a means for controlling the gaseous flow. In prior art techniques, a fan device usually circulates the air, with a suction inlet provided opposing the fan, and air outlets close to the periphery of the chamber walls, said outlets opposing the suction inlet so as to provide a flow throughout the chamber. The gaseous flow is however not further controlled.
With an appropriate shaping and distribution of the slits in said plate a laminar gaseous flow can for example be provided. Such a flow has an advantage in being evenly distributed in the sterilizer chamber and thereby improving the homogeneity of the heat distribution inside the chamber.
To create such a flow, said means could advantageously be arranged adjacent to a suction out- or inlet of a fan device for circulating said air in said sterilizer chamber. Thus the direction of the flow is instantly affected by the control means.
Advantageously, the total of the open areas of said slits corresponds generally to the area of said suction out- or inlet. This is to prevent pressure differences between different sections of the chamber.
Preferably, slits are provided in regions that are not directly opposing said suction out- or inlet. This is to ensure the desired gaseous distribution effect.
At least one slit could of course be provided opposing said suction out- or inlet.
Advantageously, a plate in which the slits are cut out can constitute said means. The plate would then be provided in the sterilizer chamber. Such a plate is relatively easily manufactured and handled, and could also be formed as an extra equipment for insertion in existing sterilizers.
The second problem mentioned in the previous paragraph is solved by a gaseous flow distribution means according to the preamble, being formed by a plate, which is provided with an outermost frame. The plate is further perforated for allowing water passage through the cover means of the plate. The slits as previously described are provided with edges that are extending longitudinally above said frame, so that air passage through said slits are possible even when the plate is filled with liquid.
Such a means is unique in allowing a circulating gaseous flow and at the same time providing an even water distribution through the perforations of the plate. The gaseous flow though the slits is ensured by the slits being provided with edges that extend longitudinally above said frame of the plate. The maximum water level of the plate will of course be limited to the height of the frame, and thus no water will obstruct the slits and then impact on the gaseous medium circulation.
By such a means, an even water (or any other liquid) distribution is realised by the perforations, and an even, preferably laminar gaseous flow is realised by the slits. The plate thus solves the two above-mentioned problems efficiently and in an easy realisable manner.